[001] This invention in general relates to an apparatus and method of joining one or more rods to disc. More particularly, this invention relates to an apparatus and method for welding one or more rods to disc of dissimilar material combination.
BACKGROUND OF THE INVENTION
[002] Generally one, two or three equally spaced round rods assembled in a disc of nonferrous material are used in nuclear applications as detector assembly. This will be used in assembly after drilling holes in the welded rods for application of flow of liquid.
[003] US 8695868 B2 discloses compositions and methods for dissimilar material welding. Method of welding dissimilar materials is considered in which an adaptor is used in an intermediate position between the dissimilar materials. Most preferred adaptors are manufactured by friction stir welding from two dissimilar materials that are identical or similar to the dissimilar materials to be welded together.
[004] This prior art relates to use of an adaptor of similar material that have to be welded.
[005] US 3452421 A discloses friction welding of dissimilar materials. In the process of friction welding dissimilar work pieces, a collet of heat

conducting material is placed in contact with the work piece which tends to produce a greater amount of upset adjacent the interface for the two work pieces to act as a heat sink and achieve a stronger friction weld. The prior art relates to use collet of heat conducting material for friction welding. In this method a collet of heat conducting material is placed in contact with the work piece to act as a heat sink to achieve a stronger friction weld whereas the proposed method use a special fixture as an attachment to hold the disc material while carrying out the friction welding operation.
OBJECTS OF THE INVENTION
[006] It is the principal object of this invention to provide an improved fixture for holding the disc on which one, two or three rods are welded by friction welding.
[007] It is a further object of the invention to maintain dimensional tolerances between the pitch of the rods in the assembly.
[008] These and further objects, features, and advantages of the present invention will become apparent from the following description, along with the accompanying figures and drawings.
SUMMARY OF THE INVENTION
[009] The present invention relates to developing special fixture and process parameters for joining dissimilar disc type material with rods.

[0010] The invention is related to development of fixture for enabling the joining of dissimilar material to meet the desired weld quality requirements using friction welding process.
[0011] Friction welding, which is a solid-state joining process that produces coalescence in materials, using the heat developed between surfaces through a combination of mechanically induced rubbing motion and applied load. In this process one of the work pieces is attached to a motor-driven unit while the other is restrained from rotation. The motor-driven work piece is rotated at a predetermined constant speed. The work pieces to be welded are forced together and then a friction welding force is applied. Heat is generated as the faying surfaces rub together. This continues for a predetermined time, or until a preset amount of axial shortening takes place. The rotational driving force is discontinued and the rotating work piece is stopped by the application of a braking force. The friction welding force is maintained, or increased, for a predetermined time after rotation ceases. The technology of joining by friction can be a suitable method for joining of dissimilar material joining requirements.
BRIEF DESCRIPTIONS OF THE ACCOMPANYING DRAWINGS
Fig.1 The disc and rod of dissimilar material to be joined
Fig. 2 Apparatus according to the present invention to hold the disc

Fig.3. Apparatus according to the present invention holding the disc
Fig.4. Loading the apparatus with disc to the slider of the welding station and the rod to be welded is set in the rotatable chuck
Fig.5 The disc after welding the centre rod
DETAIL DESCRIPTION OF THE INVENTION
[0012] The present invention will be described in detail below with reference to an embodiment as shown in the drawing.
[0013] Rod to rod and rod to disc type joints are required for instrumentation applications in detector assembly of nuclear applications. Welding of dissimilar material like aluminum disc to steel is a challenging work since the work involves welding of two or three SS rods of 10-16 mm diameter on to single aluminum disc of diameter 80-90 mm with a pitch of 20-30 mm. The rods have to be welded into the aluminum disc to get a penetration about 5-6 mm depth inside the aluminum disc.
[0014] Although the number of rods used in the assembly may vary in position, the examples in this invention will show predominantly three rod assembly sets.

[0015] The schematic side view of the complete disc to rod assembly as shown in FIG. 1, the disc (1) and the rods (2) of dissimilar material to be joined.
[0016] Ref. to Fig. 2 & 3, the apparatus according to the present invention comprises of a mounting base (4) for mounting disc (1) and a top ring (5) that allows the disc to rod (3) assembly to be fastened before taking up the assembly to welding station. The disc (1) is clamped in the apparatus with total of four screws (6), half of which are fastened from opposite directions. The bottom side of the fixture is made with attachment as rod (7) to hold the assembly in the slider side of the welding station.
[0017] Ref. to fig. 4, the rod (3) which have to be welded onto the disc (1) will be inserted in chuck (8) which is enabled to rotate when the disc which is clamped in fixture from a slider (9) side.
[0018] The heat generates at the faying surfaces of the disc assembly and the rod. The heat will be used in joining of the rod with the disc assembly when an upset force is given from slider side.
[0019] The material expelled due to frictional joining will be removed by machining.
[0020] Fig. 5 shows the disc after welding with centre rod.

[0021] Similarly the same process is repeated to weld second and third rod in the disc (1).

WE CLAIM:
1. An apparatus (10) for welding one or more rods (3) to disc(1) of
dissimilar material combination, comprising of
of a round mounting base (4) for mounting disc (1);
a top ring (5) that allows the disc (1) to be fastened before taking up said disc (1) assembly to welding station;
said disc (1) is clamped in said apparatus (10) with total of four screws (6), half of which are fastened from opposite directions; and
said mounting base (4) is made with an attachment as rod (7) to hold the assembly in the slider side of the welding station.
2. The apparatus (10) as claimed in claim 1, wherein said mounting base (4) and said top ring (5) each have 4 drill holes.
3. The apparatus (10) as claimed in claim 1, wherein the diameter of said top ring (5) is equal to said mounting base (4).
4. A method for welding one or more rods to disc of dissimilar material combination, comprising steps of
Said disc (1) is mounted on said mounting base (4); Said top ring (5) is fastened to clamp said disc (1) using 4 screws (6);

Said rod (7) holds the assembly in the slider side (9) of the welding machine;
Said rod (3) which is to be welded onto said disc (1) is inserted in a chuck (8);
Said chuck (8) is enabled to rotate when said disc (1) is clamped in said apparatus from said slider (9), which generates heat at the surfaces of said disc (1) and said rod (3);
An upset force is applied from said slider (9) which with the help of generated heat joins said rod (3) to said disc (1).